1. Field of the Invention
The present invention relates to an electric lamp of the type having a light-source capsule within an outer envelope or jacket and including a mechanical, spring-triggered elongated member which disconnects voltage to one lead of the capsule when the outer envelope or jacket is broken.
2. Description of the Prior Art
Electric lamps of the type having a light-source capsule within an outer envelope or jacket are well known in the art. For example, two commonly known electric lamps of this nature are those referred to as high intensity discharge (HID) lamps and those referred to as tungsten-halogen lamps. The present invention finds particular usefulness in the latter; that is, in tungsten-halogen lamps where a tungsten-halogen capsule is mounted within an outer jacket or envelope. One significant difference between the two is that in a conventional high intensity discharge lamp the inner envelope commonly referred to as an arc tube and the outer envelope or jacket are each hermetically sealed. By way of contrast, in a tungsten-halogen lamp, although the inner tungsten-halogen capsule is sealed the outer jacket is not. Notwithstanding this difference, each lamp shares a common problem which is the undesirable exposure of the inner arc tube or capsule should the outer jacket be broken. Any failure of the integrity of the outer envelope will comprise the safety features performed by the outer envelope. For example, in lamps of the type of the present invention if the outer jacket is damaged, the inner capsule might continue to light. Due to the high temperature and high pressure of the inner capsule the possibility that such inner capsule might shatter presents a continuing concern. The shattering of the inner capsule can cause a release of hot particles into the atmosphere which will create a risk of personal injury and property damage. It is therefore desirable to provide some means for disabling or disconnecting the power to the lamp upon sensing of such a failure in the outer envelope.
Although the present invention relates to those lamps wherein the outer envelope is not sealed, it is insightful to review the known safety features applied to the sealed outer jackets of high intensity discharge lamps, some of the concerns associated with sealed and non-sealed outer jackets being the same. In U.S. Pat. No. 4,032,816 to Rokosz, which issued on June 28, 1977, a spring loaded safety switch is connected in series with one of the electrodes of the inner bulb. Under normal operating conditions, the switch is held closed by the outer glass envelope. Breakage of the envelope will allow the switch to open and de-energize the lamp. This particular switch is mounted near the top electrode farthest from the lamp base.
In U.S. Pat. No. 4,039,893 to Corbley, which issued on Aug. 2, 1977, a mechanical disconnect switch is installed in the circuit for the upper electrode, but the switch is mounted near the bulb base and held in a closed, operative position by the contact of the upper inner lamp support with the inside of the top of the outer envelope. A spring associated with the switch will force the switch contacts apart upon breakage of the outer envelope. There will be subsequent loss of support for the upper inner lamp support.
A simple leaf spring switch protects the HID lamp in U.S. Pat. No. 4,229,678 to Petro, which issued on Oct. 21, 1980. This switch is mounted at the top of the lamp opposite the base, and is held closed by contact of one leaf with the inside of the outer envelope. Thus, breakage of the envelope will allow the switch to open and de-energize the lamp.
A similar leaf spring switch is provided in U.S. Pat. No. 4,217,522 to Strauss, which issued on Aug. 12, 1980. In a first embodiment, the spring leaves are mounted near the top of the lamp and engage the inside surface of the outer envelope just as in the Petro patent described above. A second embodiment discloses a compound curve in one of the spring leaves and a slightly different mounting arrangement.
Yet another leaf spring design is provided in U.S. Pat. No. 4,221,993 to Phillipp et al, which issued on Sept. 9, 1980. This design includes a single leaf spring switch in which the leaf is formed into a loop with both ends secured at a single mounting point, which point is also part of the supply circuit for the upper electrode of the arc tube. Under normal operating conditions, one side of the single leaf is pressed into contact with the contact button for the upper electrode by pressure generated on the other side of the leaf where it presses against the inside of the outer envelope. Consequently, breakage of the outer envelope releases the pressure, and the spring disconnects the upper electrode at its contact button.
U.S. Pat. Nos. 4,156,830 and 4,752,718 to Strauss et al, which issued on May 29, 1979 and June 21, 1988, respectively, offer further refinements of the leaf spring switch by including contact buttons on each leaf. These patents also offer another embodiment which is a recent refinement of a basic fuse safety device, in which a small filament is provided within the outer envelope, which filament will oxidize and burn out upon breakage of the envelope and exposure to the atmosphere.
Yet another embodiment of the resilient leaf spring switch is shown in U.S. Pat. No. 4,013,920 to Petro, which issued on Mar. 22, 1977. As in other switches of this type, the switch is held closed by contact of one of the leaves with the inside of the outer glass envelope. Breakage of the envelope, allows the switch contacts to separate, disconnecting the arc tube from its source of power.
In U.S. Pat. No. 4,186,327 to Petro, which issued on Jan. 29, 1980, a different type of switch is provided in the form of a thin, fragile, striplike conductor which forms part of the electrode circuitry for the arc tube. This fragile conductor is secured to the inner wall of the outer glass envelope, where it will be destroyed or broken when the envelope is broken, thus deenergizing the lamp.
In U.S. Pat. No. 4,417,177 to Laxiano, which issued on Nov. 22, 1983, a safety switch is disclosed which is specifically adapted to high intensity discharge lamps in which a vacuum is drawn within the outerglass envelope. The switch means, mounted in the base of the bulb, will remain in a closed, operative position as long as the vacuum within the outer envelope remains intact. Loss of the vacuum, as by breakage of the envelope, will release a spring biased switch activator which will open the switch and disconnect the lamp.
The present invention represents an effort to provide a spring biased automatic mechanical safety switch for electric lamps wherein the outer envelopes is not hermetically sealed. In contrast to the foregoing prior art, such switch extends out of the outer envelope and through the base, and is moveable relative thereto as described therein.